The extended Berkeley Packet Filter (eBPF) subsystem consists in
programs written in a pseudo-assembly language, then attached to one
of the several kernel hooks and run in reaction of specific events.
This framework differs from the older, "classic" BPF (or "cBPF") in
several aspects, one of them being the ability to call special
functions (or "helpers") from within a program. These functions are
restricted to a white-list of helpers defined in the kernel.
These helpers are used by eBPF programs to interact with the system,
or with the context in which they work. For instance, they can be
used to print debugging messages, to get the time since the system
was booted, to interact with eBPF maps, or to manipulate network
packets. Since there are several eBPF program types, and that they do
not run in the same context, each program type can only call a subset
of those helpers.
Due to eBPF conventions, a helper can not have more than five
arguments.
Internally, eBPF programs call directly into the compiled helper
functions without requiring any foreign-function interface. As a
result, calling helpers introduces no overhead, thus offering
excellent performance.
This document is an attempt to list and document the helpers
available to eBPF developers. They are sorted by chronological order
(the oldest helpers in the kernel at the top).

void *bpf_map_lookup_elem(struct bpf_map *map, const void *key)Description
Perform a lookup in map for an entry associated to key.
Return Map value associated to key, or NULL if no entry was
found.
int bpf_map_update_elem(struct bpf_map *map, const void *key, constvoid *value, u64 flags)Description
Add or update the value of the entry associated to key
in map with value. flags is one of:
BPF_NOEXIST
The entry for key must not exist in the map.
BPF_EXIST
The entry for key must already exist in the map.
BPF_ANY
No condition on the existence of the entry for
key.
Flag value BPF_NOEXIST cannot be used for maps of types
BPF_MAP_TYPE_ARRAY or BPF_MAP_TYPE_PERCPU_ARRAY (all
elements always exist), the helper would return an
error.
Return 0 on success, or a negative error in case of failure.
int bpf_map_delete_elem(struct bpf_map *map, const void *key)Description
Delete entry with key from map.
Return 0 on success, or a negative error in case of failure.
int bpf_map_push_elem(struct bpf_map *map, const void *value, u64flags)Description
Push an element value in map. flags is one of:
BPF_EXIST If the queue/stack is full, the oldest
element is removed to make room for this.
Return 0 on success, or a negative error in case of failure.
int bpf_probe_read(void *dst, u32 size, const void *src)Description
For tracing programs, safely attempt to read size bytes
from address src and store the data in dst.
Return 0 on success, or a negative error in case of failure.
u64 bpf_ktime_get_ns(void)Description
Return the time elapsed since system boot, in
nanoseconds.
Return Current ktime.
int bpf_trace_printk(const char *fmt, u32 fmt_size, ...)Description
This helper is a "printk()-like" facility for
debugging. It prints a message defined by format fmt
(of size fmt_size) to file
/sys/kernel/debug/tracing/trace from DebugFS, if
available. It can take up to three additional u64
arguments (as an eBPF helpers, the total number of
arguments is limited to five).
Each time the helper is called, it appends a line to
the trace. The format of the trace is customizable,
and the exact output one will get depends on the
options set in /sys/kernel/debug/tracing/trace_options
(see also the README file under the same directory).
However, it usually defaults to something like:
telnet-470 [001] .N.. 419421.045894: 0x00000001: <formatted msg>
In the above:
· telnet is the name of the current task.
· 470 is the PID of the current task.
· 001 is the CPU number on which the task is
running.
· In .N.., each character refers to a set of options
(whether irqs are enabled, scheduling options,
whether hard/softirqs are running, level of
preempt_disabled respectively). N means that
TIF_NEED_RESCHED and PREEMPT_NEED_RESCHED are set.
· 419421.045894 is a timestamp.
· 0x00000001 is a fake value used by BPF for the
instruction pointer register.
· <formatted msg> is the message formatted with fmt.
The conversion specifiers supported by fmt are similar,
but more limited than for printk(). They are %d, %i,
%u, %x, %ld, %li, %lu, %lx, %lld, %lli, %llu, %llx, %p,
%s. No modifier (size of field, padding with zeroes,
etc.) is available, and the helper will return -EINVAL
(but print nothing) if it encounters an unknown
specifier.
Also, note that bpf_trace_printk() is slow, and should
only be used for debugging purposes. For this reason, a
notice bloc (spanning several lines) is printed to
kernel logs and states that the helper should not be
used "for production use" the first time this helper is
used (or more precisely, when trace_printk() buffers
are allocated). For passing values to user space, perf
events should be preferred.
Return The number of bytes written to the buffer, or a
negative error in case of failure.
u32 bpf_get_prandom_u32(void)Description
Get a pseudo-random number.
From a security point of view, this helper uses its own
pseudo-random internal state, and cannot be used to
infer the seed of other random functions in the kernel.
However, it is essential to note that the generator
used by the helper is not cryptographically secure.
Return A random 32-bit unsigned value.
u32 bpf_get_smp_processor_id(void)Description
Get the SMP (symmetric multiprocessing) processor id.
Note that all programs run with preemption disabled,
which means that the SMP processor id is stable during
all the execution of the program.
Return The SMP id of the processor running the program.
int bpf_skb_store_bytes(struct sk_buff *skb, u32 offset, const void*from, u32 len, u64 flags)Description
Store len bytes from address from into the packet
associated to skb, at offset. flags are a combination
of BPF_F_RECOMPUTE_CSUM (automatically recompute the
checksum for the packet after storing the bytes) and
BPF_F_INVALIDATE_HASH (set skb->hash, skb->swhash and
skb->l4hash to 0).
A call to this helper is susceptible to change the
underlaying packet buffer. Therefore, at load time, all
checks on pointers previously done by the verifier are
invalidated and must be performed again, if the helper
is used in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
int bpf_l3_csum_replace(struct sk_buff *skb, u32 offset, u64 from,u64 to, u64 size)Description
Recompute the layer 3 (e.g. IP) checksum for the packet
associated to skb. Computation is incremental, so the
helper must know the former value of the header field
that was modified (from), the new value of this field
(to), and the number of bytes (2 or 4) for this field,
stored in size. Alternatively, it is possible to store
the difference between the previous and the new values
of the header field in to, by setting from and size to
0. For both methods, offset indicates the location of
the IP checksum within the packet.
This helper works in combination with bpf_csum_diff(),
which does not update the checksum in-place, but offers
more flexibility and can handle sizes larger than 2 or
4 for the checksum to update.
A call to this helper is susceptible to change the
underlaying packet buffer. Therefore, at load time, all
checks on pointers previously done by the verifier are
invalidated and must be performed again, if the helper
is used in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
int bpf_l4_csum_replace(struct sk_buff *skb, u32 offset, u64 from,u64 to, u64 flags)Description
Recompute the layer 4 (e.g. TCP, UDP or ICMP) checksum
for the packet associated to skb. Computation is
incremental, so the helper must know the former value
of the header field that was modified (from), the new
value of this field (to), and the number of bytes (2 or
4) for this field, stored on the lowest four bits of
flags. Alternatively, it is possible to store the
difference between the previous and the new values of
the header field in to, by setting from and the four
lowest bits of flags to 0. For both methods, offset
indicates the location of the IP checksum within the
packet. In addition to the size of the field, flags can
be added (bitwise OR) actual flags. With
BPF_F_MARK_MANGLED_0, a null checksum is left untouched
(unless BPF_F_MARK_ENFORCE is added as well), and for
updates resulting in a null checksum the value is set
to CSUM_MANGLED_0 instead. Flag BPF_F_PSEUDO_HDR
indicates the checksum is to be computed against a
pseudo-header.
This helper works in combination with bpf_csum_diff(),
which does not update the checksum in-place, but offers
more flexibility and can handle sizes larger than 2 or
4 for the checksum to update.
A call to this helper is susceptible to change the
underlaying packet buffer. Therefore, at load time, all
checks on pointers previously done by the verifier are
invalidated and must be performed again, if the helper
is used in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
int bpf_tail_call(void *ctx, struct bpf_map *prog_array_map, u32index)Description
This special helper is used to trigger a "tail call",
or in other words, to jump into another eBPF program.
The same stack frame is used (but values on stack and
in registers for the caller are not accessible to the
callee). This mechanism allows for program chaining,
either for raising the maximum number of available eBPF
instructions, or to execute given programs in
conditional blocks. For security reasons, there is an
upper limit to the number of successive tail calls that
can be performed.
Upon call of this helper, the program attempts to jump
into a program referenced at index index in
prog_array_map, a special map of type
BPF_MAP_TYPE_PROG_ARRAY, and passes ctx, a pointer to
the context.
If the call succeeds, the kernel immediately runs the
first instruction of the new program. This is not a
function call, and it never returns to the previous
program. If the call fails, then the helper has no
effect, and the caller continues to run its subsequent
instructions. A call can fail if the destination
program for the jump does not exist (i.e. index is
superior to the number of entries in prog_array_map),
or if the maximum number of tail calls has been reached
for this chain of programs. This limit is defined in
the kernel by the macro MAX_TAIL_CALL_CNT (not
accessible to user space), which is currently set to
32.
Return 0 on success, or a negative error in case of failure.
int bpf_clone_redirect(struct sk_buff *skb, u32 ifindex, u64 flags)Description
Clone and redirect the packet associated to skb to
another net device of index ifindex. Both ingress and
egress interfaces can be used for redirection. The
BPF_F_INGRESS value in flags is used to make the
distinction (ingress path is selected if the flag is
present, egress path otherwise). This is the only flag
supported for now.
In comparison with bpf_redirect() helper,
bpf_clone_redirect() has the associated cost of
duplicating the packet buffer, but this can be executed
out of the eBPF program. Conversely, bpf_redirect() is
more efficient, but it is handled through an action
code where the redirection happens only after the eBPF
program has returned.
A call to this helper is susceptible to change the
underlaying packet buffer. Therefore, at load time, all
checks on pointers previously done by the verifier are
invalidated and must be performed again, if the helper
is used in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
u64 bpf_get_current_pid_tgid(void)Return A 64-bit integer containing the current tgid and pid,
and created as such: current_task->tgid << 32 |current_task->pid.
u64 bpf_get_current_uid_gid(void)Return A 64-bit integer containing the current GID and UID,
and created as such: current_gid<< 32 | current_uid.
int bpf_get_current_comm(char *buf, u32 size_of_buf)Description
Copy the comm attribute of the current task into buf of
size_of_buf. The comm attribute contains the name of
the executable (excluding the path) for the current
task. The size_of_buf must be strictly positive. On
success, the helper makes sure that the buf is
NUL-terminated. On failure, it is filled with zeroes.
Return 0 on success, or a negative error in case of failure.
u32 bpf_get_cgroup_classid(struct sk_buff *skb)Description
Retrieve the classid for the current task, i.e. for the
net_cls cgroup to which skb belongs.
This helper can be used on TC egress path, but not on
ingress.
The net_cls cgroup provides an interface to tag network
packets based on a user-provided identifier for all
traffic coming from the tasks belonging to the related
cgroup. See also the related kernel documentation,
available from the Linux sources in file
Documentation/cgroup-v1/net_cls.txt.
The Linux kernel has two versions for cgroups: there
are cgroups v1 and cgroups v2. Both are available to
users, who can use a mixture of them, but note that the
net_cls cgroup is for cgroup v1 only. This makes it
incompatible with BPF programs run on cgroups, which is
a cgroup-v2-only feature (a socket can only hold data
for one version of cgroups at a time).
This helper is only available is the kernel was
compiled with the CONFIG_CGROUP_NET_CLASSID
configuration option set to "y" or to "m".
Return The classid, or 0 for the default unconfigured classid.
int bpf_skb_vlan_push(struct sk_buff *skb, __be16 vlan_proto, u16vlan_tci)Description
Push a vlan_tci (VLAN tag control information) of
protocol vlan_proto to the packet associated to skb,
then update the checksum. Note that if vlan_proto is
different from ETH_P_8021Q and ETH_P_8021AD, it is
considered to be ETH_P_8021Q.
A call to this helper is susceptible to change the
underlaying packet buffer. Therefore, at load time, all
checks on pointers previously done by the verifier are
invalidated and must be performed again, if the helper
is used in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
int bpf_skb_vlan_pop(struct sk_buff *skb)Description
Pop a VLAN header from the packet associated to skb.
A call to this helper is susceptible to change the
underlaying packet buffer. Therefore, at load time, all
checks on pointers previously done by the verifier are
invalidated and must be performed again, if the helper
is used in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
int bpf_skb_get_tunnel_key(struct sk_buff *skb, struct bpf_tunnel_key*key, u32 size, u64 flags)Description
Get tunnel metadata. This helper takes a pointer key to
an empty struct bpf_tunnel_key of size, that will be
filled with tunnel metadata for the packet associated
to skb. The flags can be set to BPF_F_TUNINFO_IPV6,
which indicates that the tunnel is based on IPv6
protocol instead of IPv4.
The struct bpf_tunnel_key is an object that generalizes
the principal parameters used by various tunneling
protocols into a single struct. This way, it can be
used to easily make a decision based on the contents of
the encapsulation header, "summarized" in this struct.
In particular, it holds the IP address of the remote
end (IPv4 or IPv6, depending on the case) in
key->remote_ipv4 or key->remote_ipv6. Also, this struct
exposes the key->tunnel_id, which is generally mapped
to a VNI (Virtual Network Identifier), making it
programmable together with the bpf_skb_set_tunnel_key()
helper.
Let's imagine that the following code is part of a
program attached to the TC ingress interface, on one
end of a GRE tunnel, and is supposed to filter out all
messages coming from remote ends with IPv4 address
other than 10.0.0.1:
int ret;
struct bpf_tunnel_key key = {};
ret = bpf_skb_get_tunnel_key(skb, &key, sizeof(key), 0);
if (ret < 0)
return TC_ACT_SHOT; // drop packet
if (key.remote_ipv4 != 0x0a000001)
return TC_ACT_SHOT; // drop packet
return TC_ACT_OK; // accept packet
This interface can also be used with all encapsulation
devices that can operate in "collect metadata" mode:
instead of having one network device per specific
configuration, the "collect metadata" mode only
requires a single device where the configuration can be
extracted from this helper.
This can be used together with various tunnels such as
VXLan, Geneve, GRE or IP in IP (IPIP).
Return 0 on success, or a negative error in case of failure.
int bpf_skb_set_tunnel_key(struct sk_buff *skb, struct bpf_tunnel_key*key, u32 size, u64 flags)Description
Populate tunnel metadata for packet associated to skb.
The tunnel metadata is set to the contents of key, of
size. The flags can be set to a combination of the
following values:
BPF_F_TUNINFO_IPV6
Indicate that the tunnel is based on IPv6
protocol instead of IPv4.
BPF_F_ZERO_CSUM_TX
For IPv4 packets, add a flag to tunnel metadata
indicating that checksum computation should be
skipped and checksum set to zeroes.
BPF_F_DONT_FRAGMENT
Add a flag to tunnel metadata indicating that
the packet should not be fragmented.
BPF_F_SEQ_NUMBER
Add a flag to tunnel metadata indicating that a
sequence number should be added to tunnel header
before sending the packet. This flag was added
for GRE encapsulation, but might be used with
other protocols as well in the future.
Here is a typical usage on the transmit path:
struct bpf_tunnel_key key;
populate key ...
bpf_skb_set_tunnel_key(skb, &key, sizeof(key), 0);
bpf_clone_redirect(skb, vxlan_dev_ifindex, 0);
See also the description of the
bpf_skb_get_tunnel_key() helper for additional
information.
Return 0 on success, or a negative error in case of failure.
u64 bpf_perf_event_read(struct bpf_map *map, u64 flags)Description
Read the value of a perf event counter. This helper
relies on a map of type BPF_MAP_TYPE_PERF_EVENT_ARRAY.
The nature of the perf event counter is selected when
map is updated with perf event file descriptors. The
map is an array whose size is the number of available
CPUs, and each cell contains a value relative to one
CPU. The value to retrieve is indicated by flags, that
contains the index of the CPU to look up, masked with
BPF_F_INDEX_MASK. Alternatively, flags can be set to
BPF_F_CURRENT_CPU to indicate that the value for the
current CPU should be retrieved.
Note that before Linux 4.13, only hardware perf event
can be retrieved.
Also, be aware that the newer helper
bpf_perf_event_read_value() is recommended over
bpf_perf_event_read() in general. The latter has some
ABI quirks where error and counter value are used as a
return code (which is wrong to do since ranges may
overlap). This issue is fixed with
bpf_perf_event_read_value(), which at the same time
provides more features over the bpf_perf_event_read()
interface. Please refer to the description of
bpf_perf_event_read_value() for details.
Return The value of the perf event counter read from the map,
or a negative error code in case of failure.
int bpf_redirect(u32 ifindex, u64 flags)Description
Redirect the packet to another net device of index
ifindex. This helper is somewhat similar to
bpf_clone_redirect(), except that the packet is not
cloned, which provides increased performance.
Except for XDP, both ingress and egress interfaces can
be used for redirection. The BPF_F_INGRESS value in
flags is used to make the distinction (ingress path is
selected if the flag is present, egress path
otherwise). Currently, XDP only supports redirection to
the egress interface, and accepts no flag at all.
The same effect can be attained with the more generic
bpf_redirect_map(), which requires specific maps to be
used but offers better performance.
Return For XDP, the helper returns XDP_REDIRECT on success or
XDP_ABORTED on error. For other program types, the
values are TC_ACT_REDIRECT on success or TC_ACT_SHOT on
error.
u32 bpf_get_route_realm(struct sk_buff *skb)Description
Retrieve the realm or the route, that is to say the
tclassid field of the destination for the skb. The
indentifier retrieved is a user-provided tag, similar
to the one used with the net_cls cgroup (see
description for bpf_get_cgroup_classid() helper), but
here this tag is held by a route (a destination entry),
not by a task.
Retrieving this identifier works with the clsact TC
egress hook (see also tc-bpf(8)), or alternatively on
conventional classful egress qdiscs, but not on TC
ingress path. In case of clsact TC egress hook, this
has the advantage that, internally, the destination
entry has not been dropped yet in the transmit path.
Therefore, the destination entry does not need to be
artificially held via netif_keep_dst() for a classful
qdisc until the skb is freed.
This helper is available only if the kernel was
compiled with CONFIG_IP_ROUTE_CLASSID configuration
option.
Return The realm of the route for the packet associated to
skb, or 0 if none was found.
int bpf_perf_event_output(struct pt_reg *ctx, struct bpf_map *map,u64 flags, void *data, u64 size)Description
Write raw data blob into a special BPF perf event held
by map of type BPF_MAP_TYPE_PERF_EVENT_ARRAY. This perf
event must have the following attributes:
PERF_SAMPLE_RAW as sample_type, PERF_TYPE_SOFTWARE as
type, and PERF_COUNT_SW_BPF_OUTPUT as config.
The flags are used to indicate the index in map for
which the value must be put, masked with
BPF_F_INDEX_MASK. Alternatively, flags can be set to
BPF_F_CURRENT_CPU to indicate that the index of the
current CPU core should be used.
The value to write, of size, is passed through eBPF
stack and pointed by data.
The context of the program ctx needs also be passed to
the helper.
On user space, a program willing to read the values
needs to call perf_event_open() on the perf event
(either for one or for all CPUs) and to store the file
descriptor into the map. This must be done before the
eBPF program can send data into it. An example is
available in file samples/bpf/trace_output_user.c in
the Linux kernel source tree (the eBPF program
counterpart is in samples/bpf/trace_output_kern.c).
bpf_perf_event_output() achieves better performance
than bpf_trace_printk() for sharing data with user
space, and is much better suitable for streaming data
from eBPF programs.
Note that this helper is not restricted to tracing use
cases and can be used with programs attached to TC or
XDP as well, where it allows for passing data to user
space listeners. Data can be:
· Only custom structs,
· Only the packet payload, or
· A combination of both.
Return 0 on success, or a negative error in case of failure.
int bpf_skb_load_bytes(const struct sk_buff *skb, u32 offset, void*to, u32 len)Description
This helper was provided as an easy way to load data
from a packet. It can be used to load len bytes from
offset from the packet associated to skb, into the
buffer pointed by to.
Since Linux 4.7, usage of this helper has mostly been
replaced by "direct packet access", enabling packet
data to be manipulated with skb->data and skb->data_end
pointing respectively to the first byte of packet data
and to the byte after the last byte of packet data.
However, it remains useful if one wishes to read large
quantities of data at once from a packet into the eBPF
stack.
Return 0 on success, or a negative error in case of failure.
int bpf_get_stackid(struct pt_reg *ctx, struct bpf_map *map, u64flags)Description
Walk a user or a kernel stack and return its id. To
achieve this, the helper needs ctx, which is a pointer
to the context on which the tracing program is
executed, and a pointer to a map of type
BPF_MAP_TYPE_STACK_TRACE.
The last argument, flags, holds the number of stack
frames to skip (from 0 to 255), masked with
BPF_F_SKIP_FIELD_MASK. The next bits can be used to set
a combination of the following flags:
BPF_F_USER_STACK
Collect a user space stack instead of a kernel
stack.
BPF_F_FAST_STACK_CMP
Compare stacks by hash only.
BPF_F_REUSE_STACKID
If two different stacks hash into the same
stackid, discard the old one.
The stack id retrieved is a 32 bit long integer handle
which can be further combined with other data
(including other stack ids) and used as a key into
maps. This can be useful for generating a variety of
graphs (such as flame graphs or off-cpu graphs).
For walking a stack, this helper is an improvement over
bpf_probe_read(), which can be used with unrolled loops
but is not efficient and consumes a lot of eBPF
instructions. Instead, bpf_get_stackid() can collect
up to PERF_MAX_STACK_DEPTH both kernel and user frames.
Note that this limit can be controlled with the sysctl
program, and that it should be manually increased in
order to profile long user stacks (such as stacks for
Java programs). To do so, use:
# sysctl kernel.perf_event_max_stack=<new value>
Return The positive or null stack id on success, or a negative
error in case of failure.
s64 bpf_csum_diff(__be32 *from, u32 from_size, __be32 *to, u32to_size, __wsum seed)Description
Compute a checksum difference, from the raw buffer
pointed by from, of length from_size (that must be a
multiple of 4), towards the raw buffer pointed by to,
of size to_size (same remark). An optional seed can be
added to the value (this can be cascaded, the seed may
come from a previous call to the helper).
This is flexible enough to be used in several ways:
· With from_size == 0, to_size > 0 and seed set to
checksum, it can be used when pushing new data.
· With from_size > 0, to_size == 0 and seed set to
checksum, it can be used when removing data from a
packet.
· With from_size > 0, to_size > 0 and seed set to 0, it
can be used to compute a diff. Note that from_size
and to_size do not need to be equal.
This helper can be used in combination with
bpf_l3_csum_replace() and bpf_l4_csum_replace(), to
which one can feed in the difference computed with
bpf_csum_diff().
Return The checksum result, or a negative error code in case
of failure.
int bpf_skb_get_tunnel_opt(struct sk_buff *skb, u8 *opt, u32 size)Description
Retrieve tunnel options metadata for the packet
associated to skb, and store the raw tunnel option data
to the buffer opt of size.
This helper can be used with encapsulation devices that
can operate in "collect metadata" mode (please refer to
the related note in the description of
bpf_skb_get_tunnel_key() for more details). A
particular example where this can be used is in
combination with the Geneve encapsulation protocol,
where it allows for pushing (with
bpf_skb_get_tunnel_opt() helper) and retrieving
arbitrary TLVs (Type-Length-Value headers) from the
eBPF program. This allows for full customization of
these headers.
Return The size of the option data retrieved.
int bpf_skb_set_tunnel_opt(struct sk_buff *skb, u8 *opt, u32 size)Description
Set tunnel options metadata for the packet associated
to skb to the option data contained in the raw buffer
opt of size.
See also the description of the
bpf_skb_get_tunnel_opt() helper for additional
information.
Return 0 on success, or a negative error in case of failure.
int bpf_skb_change_proto(struct sk_buff *skb, __be16 proto, u64flags)Description
Change the protocol of the skb to proto. Currently
supported are transition from IPv4 to IPv6, and from
IPv6 to IPv4. The helper takes care of the groundwork
for the transition, including resizing the socket
buffer. The eBPF program is expected to fill the new
headers, if any, via skb_store_bytes() and to recompute
the checksums with bpf_l3_csum_replace() and
bpf_l4_csum_replace(). The main case for this helper is
to perform NAT64 operations out of an eBPF program.
Internally, the GSO type is marked as dodgy so that
headers are checked and segments are recalculated by
the GSO/GRO engine. The size for GSO target is adapted
as well.
All values for flags are reserved for future usage, and
must be left at zero.
A call to this helper is susceptible to change the
underlaying packet buffer. Therefore, at load time, all
checks on pointers previously done by the verifier are
invalidated and must be performed again, if the helper
is used in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
int bpf_skb_change_type(struct sk_buff *skb, u32 type)Description
Change the packet type for the packet associated to
skb. This comes down to setting skb->pkt_type to type,
except the eBPF program does not have a write access to
skb->pkt_type beside this helper. Using a helper here
allows for graceful handling of errors.
The major use case is to change incoming skb*s to**PACKET_HOST* in a programmatic way instead of having
to recirculate via redirect(..., BPF_F_INGRESS), for
example.
Note that type only allows certain values. At this
time, they are:
PACKET_HOST
Packet is for us.
PACKET_BROADCAST
Send packet to all.
PACKET_MULTICAST
Send packet to group.
PACKET_OTHERHOST
Send packet to someone else.
Return 0 on success, or a negative error in case of failure.
int bpf_skb_under_cgroup(struct sk_buff *skb, struct bpf_map *map,u32 index)Description
Check whether skb is a descendant of the cgroup2 held
by map of type BPF_MAP_TYPE_CGROUP_ARRAY, at index.
Return The return value depends on the result of the test, and
can be:
· 0, if the skb failed the cgroup2 descendant test.
· 1, if the skb succeeded the cgroup2 descendant test.
· A negative error code, if an error occurred.
u32 bpf_get_hash_recalc(struct sk_buff *skb)Description
Retrieve the hash of the packet, skb->hash. If it is
not set, in particular if the hash was cleared due to
mangling, recompute this hash. Later accesses to the
hash can be done directly with skb->hash.
Calling bpf_set_hash_invalid(), changing a packet
prototype with bpf_skb_change_proto(), or calling
bpf_skb_store_bytes() with the BPF_F_INVALIDATE_HASH
are actions susceptible to clear the hash and to
trigger a new computation for the next call to
bpf_get_hash_recalc().
Return The 32-bit hash.
u64 bpf_get_current_task(void)Return A pointer to the current task struct.
int bpf_probe_write_user(void *dst, const void *src, u32 len)Description
Attempt in a safe way to write len bytes from the
buffer src to dst in memory. It only works for threads
that are in user context, and dst must be a valid user
space address.
This helper should not be used to implement any kind of
security mechanism because of TOC-TOU attacks, but
rather to debug, divert, and manipulate execution of
semi-cooperative processes.
Keep in mind that this feature is meant for
experiments, and it has a risk of crashing the system
and running programs. Therefore, when an eBPF program
using this helper is attached, a warning including PID
and process name is printed to kernel logs.
Return 0 on success, or a negative error in case of failure.
int bpf_current_task_under_cgroup(struct bpf_map *map, u32 index)Description
Check whether the probe is being run is the context of
a given subset of the cgroup2 hierarchy. The cgroup2 to
test is held by map of type BPF_MAP_TYPE_CGROUP_ARRAY,
at index.
Return The return value depends on the result of the test, and
can be:
· 0, if the skb task belongs to the cgroup2.
· 1, if the skb task does not belong to the cgroup2.
· A negative error code, if an error occurred.
int bpf_skb_change_tail(struct sk_buff *skb, u32 len, u64 flags)Description
Resize (trim or grow) the packet associated to skb to
the new len. The flags are reserved for future usage,
and must be left at zero.
The basic idea is that the helper performs the needed
work to change the size of the packet, then the eBPF
program rewrites the rest via helpers like
bpf_skb_store_bytes(), bpf_l3_csum_replace(),
bpf_l3_csum_replace() and others. This helper is a slow
path utility intended for replies with control
messages. And because it is targeted for slow path, the
helper itself can afford to be slow: it implicitly
linearizes, unclones and drops offloads from the skb.
A call to this helper is susceptible to change the
underlaying packet buffer. Therefore, at load time, all
checks on pointers previously done by the verifier are
invalidated and must be performed again, if the helper
is used in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
int bpf_skb_pull_data(struct sk_buff *skb, u32 len)Description
Pull in non-linear data in case the skb is non-linear
and not all of len are part of the linear section. Make
len bytes from skb readable and writable. If a zero
value is passed for len, then the whole length of the
skb is pulled.
This helper is only needed for reading and writing with
direct packet access.
For direct packet access, testing that offsets to
access are within packet boundaries (test on
skb->data_end) is susceptible to fail if offsets are
invalid, or if the requested data is in non-linear
parts of the skb. On failure the program can just bail
out, or in the case of a non-linear buffer, use a
helper to make the data available. The
bpf_skb_load_bytes() helper is a first solution to
access the data. Another one consists in using
bpf_skb_pull_data to pull in once the non-linear parts,
then retesting and eventually access the data.
At the same time, this also makes sure the skb is
uncloned, which is a necessary condition for direct
write. As this needs to be an invariant for the write
part only, the verifier detects writes and adds a
prologue that is calling bpf_skb_pull_data() to
effectively unclone the skb from the very beginning in
case it is indeed cloned.
A call to this helper is susceptible to change the
underlaying packet buffer. Therefore, at load time, all
checks on pointers previously done by the verifier are
invalidated and must be performed again, if the helper
is used in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
s64 bpf_csum_update(struct sk_buff *skb, __wsum csum)Description
Add the checksum csum into skb->csum in case the driver
has supplied a checksum for the entire packet into that
field. Return an error otherwise. This helper is
intended to be used in combination with
bpf_csum_diff(), in particular when the checksum needs
to be updated after data has been written into the
packet through direct packet access.
Return The checksum on success, or a negative error code in
case of failure.
void bpf_set_hash_invalid(struct sk_buff *skb)Description
Invalidate the current skb->hash. It can be used after
mangling on headers through direct packet access, in
order to indicate that the hash is outdated and to
trigger a recalculation the next time the kernel tries
to access this hash or when the bpf_get_hash_recalc()
helper is called.
int bpf_get_numa_node_id(void)Description
Return the id of the current NUMA node. The primary use
case for this helper is the selection of sockets for
the local NUMA node, when the program is attached to
sockets using the SO_ATTACH_REUSEPORT_EBPF option (see
also socket(7)), but the helper is also available to
other eBPF program types, similarly to
bpf_get_smp_processor_id().
Return The id of current NUMA node.
int bpf_skb_change_head(struct sk_buff *skb, u32 len, u64 flags)Description
Grows headroom of packet associated to skb and adjusts
the offset of the MAC header accordingly, adding len
bytes of space. It automatically extends and
reallocates memory as required.
This helper can be used on a layer 3 skb to push a MAC
header for redirection into a layer 2 device.
All values for flags are reserved for future usage, and
must be left at zero.
A call to this helper is susceptible to change the
underlaying packet buffer. Therefore, at load time, all
checks on pointers previously done by the verifier are
invalidated and must be performed again, if the helper
is used in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
int bpf_xdp_adjust_head(struct xdp_buff *xdp_md, int delta)Description
Adjust (move) xdp_md->data by delta bytes. Note that it
is possible to use a negative value for delta. This
helper can be used to prepare the packet for pushing or
popping headers.
A call to this helper is susceptible to change the
underlaying packet buffer. Therefore, at load time, all
checks on pointers previously done by the verifier are
invalidated and must be performed again, if the helper
is used in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
int bpf_probe_read_str(void *dst, int size, const void *unsafe_ptr)Description
Copy a NUL terminated string from an unsafe address
unsafe_ptr to dst. The size should include the
terminating NUL byte. In case the string length is
smaller than size, the target is not padded with
further NUL bytes. If the string length is larger than
size, just size-1 bytes are copied and the last byte is
set to NUL.
On success, the length of the copied string is
returned. This makes this helper useful in tracing
programs for reading strings, and more importantly to
get its length at runtime. See the following snippet:
SEC("kprobe/sys_open")
void bpf_sys_open(struct pt_regs *ctx)
char buf[PATHLEN]; // PATHLEN is defined to 256
int res = bpf_probe_read_str(buf, sizeof(buf),
ctx->di);
// Consume buf, for example push it to
// userspace via bpf_perf_event_output(); we
// can use res (the string length) as event
// size, after checking its boundaries.
In comparison, using bpf_probe_read() helper here
instead to read the string would require to estimate
the length at compile time, and would often result in
copying more memory than necessary.
Another useful use case is when parsing individual
process arguments or individual environment variables
navigating current->mm->arg_start and
current->mm->env_start: using this helper and the
return value, one can quickly iterate at the right
offset of the memory area.
Return On success, the strictly positive length of the string,
including the trailing NUL character. On error, a
negative value.
u64 bpf_get_socket_cookie(struct sk_buff *skb)Description
If the struct sk_buff pointed by skb has a known
socket, retrieve the cookie (generated by the kernel)
of this socket. If no cookie has been set yet,
generate a new cookie. Once generated, the socket
cookie remains stable for the life of the socket. This
helper can be useful for monitoring per socket
networking traffic statistics as it provides a unique
socket identifier per namespace.
Return A 8-byte long non-decreasing number on success, or 0 if
the socket field is missing inside skb.
u64 bpf_get_socket_cookie(struct bpf_sock_addr *ctx)Description
Equivalent to bpf_get_socket_cookie() helper that
accepts skb, but gets socket from struct bpf_sock_addr
contex.
Return A 8-byte long non-decreasing number.
u64 bpf_get_socket_cookie(struct bpf_sock_ops *ctx)Description
Equivalent to bpf_get_socket_cookie() helper that
accepts skb, but gets socket from struct bpf_sock_ops
contex.
Return A 8-byte long non-decreasing number.
u32 bpf_get_socket_uid(struct sk_buff *skb)Return The owner UID of the socket associated to skb. If the
socket is NULL, or if it is not a full socket (i.e. if
it is a time-wait or a request socket instead),
overflowuid value is returned (note that overflowuid
might also be the actual UID value for the socket).
u32 bpf_set_hash(struct sk_buff *skb, u32 hash)Description
Set the full hash for skb (set the field skb->hash) to
value hash.
Returnint bpf_setsockopt(struct bpf_sock_ops *bpf_socket, int level, intoptname, char *optval, int optlen)Description
Emulate a call to setsockopt() on the socket associated
to bpf_socket, which must be a full socket. The level
at which the option resides and the name optname of the
option must be specified, see setsockopt(2) for more
information. The option value of length optlen is
pointed by optval.
This helper actually implements a subset of
setsockopt(). It supports the following levels:
· SOL_SOCKET, which supports the following optnames:
SO_RCVBUF, SO_SNDBUF, SO_MAX_PACING_RATE,
SO_PRIORITY, SO_RCVLOWAT, SO_MARK.
· IPPROTO_TCP, which supports the following optnames:
TCP_CONGESTION, TCP_BPF_IW, TCP_BPF_SNDCWND_CLAMP.
· IPPROTO_IP, which supports optnameIP_TOS.
· IPPROTO_IPV6, which supports optnameIPV6_TCLASS.
Return 0 on success, or a negative error in case of failure.
int bpf_skb_adjust_room(struct sk_buff *skb, s32 len_diff, u32 mode,u64 flags)Description
Grow or shrink the room for data in the packet
associated to skb by len_diff, and according to the
selected mode.
There is a single supported mode at this time:
· BPF_ADJ_ROOM_NET: Adjust room at the network layer
(room space is added or removed below the layer 3
header).
All values for flags are reserved for future usage, and
must be left at zero.
A call to this helper is susceptible to change the
underlaying packet buffer. Therefore, at load time, all
checks on pointers previously done by the verifier are
invalidated and must be performed again, if the helper
is used in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
int bpf_redirect_map(struct bpf_map *map, u32 key, u64 flags)Description
Redirect the packet to the endpoint referenced by map
at index key. Depending on its type, this map can
contain references to net devices (for forwarding
packets through other ports), or to CPUs (for
redirecting XDP frames to another CPU; but this is only
implemented for native XDP (with driver support) as of
this writing).
All values for flags are reserved for future usage, and
must be left at zero.
When used to redirect packets to net devices, this
helper provides a high performance increase over
bpf_redirect(). This is due to various implementation
details of the underlying mechanisms, one of which is
the fact that bpf_redirect_map() tries to send packet
as a "bulk" to the device.
Return XDP_REDIRECT on success, or XDP_ABORTED on error.
int bpf_sk_redirect_map(struct bpf_map *map, u32 key, u64 flags)Description
Redirect the packet to the socket referenced by map (of
type BPF_MAP_TYPE_SOCKMAP) at index key. Both ingress
and egress interfaces can be used for redirection. The
BPF_F_INGRESS value in flags is used to make the
distinction (ingress path is selected if the flag is
present, egress path otherwise). This is the only flag
supported for now.
Return SK_PASS on success, or SK_DROP on error.
int bpf_sock_map_update(struct bpf_sock_ops *skops, struct bpf_map*map, void *key, u64 flags)Description
Add an entry to, or update a map referencing sockets.
The skops is used as a new value for the entry
associated to key. flags is one of:
BPF_NOEXIST
The entry for key must not exist in the map.
BPF_EXIST
The entry for key must already exist in the map.
BPF_ANY
No condition on the existence of the entry for
key.
If the map has eBPF programs (parser and verdict),
those will be inherited by the socket being added. If
the socket is already attached to eBPF programs, this
results in an error.
Return 0 on success, or a negative error in case of failure.
int bpf_xdp_adjust_meta(struct xdp_buff *xdp_md, int delta)Description
Adjust the address pointed by xdp_md->data_meta by
delta (which can be positive or negative). Note that
this operation modifies the address stored in
xdp_md->data, so the latter must be loaded only after
the helper has been called.
The use of xdp_md->data_meta is optional and programs
are not required to use it. The rationale is that when
the packet is processed with XDP (e.g. as DoS filter),
it is possible to push further meta data along with it
before passing to the stack, and to give the guarantee
that an ingress eBPF program attached as a TC
classifier on the same device can pick this up for
further post-processing. Since TC works with socket
buffers, it remains possible to set from XDP the mark
or priority pointers, or other pointers for the socket
buffer. Having this scratch space generic and
programmable allows for more flexibility as the user is
free to store whatever meta data they need.
A call to this helper is susceptible to change the
underlaying packet buffer. Therefore, at load time, all
checks on pointers previously done by the verifier are
invalidated and must be performed again, if the helper
is used in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
int bpf_perf_event_read_value(struct bpf_map *map, u64 flags, structbpf_perf_event_value *buf, u32 buf_size)Description
Read the value of a perf event counter, and store it
into buf of size buf_size. This helper relies on a map
of type BPF_MAP_TYPE_PERF_EVENT_ARRAY. The nature of
the perf event counter is selected when map is updated
with perf event file descriptors. The map is an array
whose size is the number of available CPUs, and each
cell contains a value relative to one CPU. The value to
retrieve is indicated by flags, that contains the index
of the CPU to look up, masked with BPF_F_INDEX_MASK.
Alternatively, flags can be set to BPF_F_CURRENT_CPU to
indicate that the value for the current CPU should be
retrieved.
This helper behaves in a way close to
bpf_perf_event_read() helper, save that instead of just
returning the value observed, it fills the buf
structure. This allows for additional data to be
retrieved: in particular, the enabled and running times
(in buf->enabled and buf->running, respectively) are
copied. In general, bpf_perf_event_read_value() is
recommended over bpf_perf_event_read(), which has some
ABI issues and provides fewer functionalities.
These values are interesting, because hardware PMU
(Performance Monitoring Unit) counters are limited
resources. When there are more PMU based perf events
opened than available counters, kernel will multiplex
these events so each event gets certain percentage (but
not all) of the PMU time. In case that multiplexing
happens, the number of samples or counter value will
not reflect the case compared to when no multiplexing
occurs. This makes comparison between different runs
difficult. Typically, the counter value should be
normalized before comparing to other experiments. The
usual normalization is done as follows.
normalized_counter = counter * t_enabled / t_running
Where t_enabled is the time enabled for event and
t_running is the time running for event since last
normalization. The enabled and running times are
accumulated since the perf event open. To achieve
scaling factor between two invocations of an eBPF
program, users can can use CPU id as the key (which is
typical for perf array usage model) to remember the
previous value and do the calculation inside the eBPF
program.
Return 0 on success, or a negative error in case of failure.
int bpf_perf_prog_read_value(struct bpf_perf_event_data *ctx, structbpf_perf_event_value *buf, u32 buf_size)Description
For en eBPF program attached to a perf event, retrieve
the value of the event counter associated to ctx and
store it in the structure pointed by buf and of size
buf_size. Enabled and running times are also stored in
the structure (see description of helper
bpf_perf_event_read_value() for more details).
Return 0 on success, or a negative error in case of failure.
int bpf_getsockopt(struct bpf_sock_ops *bpf_socket, int level, intoptname, char *optval, int optlen)Description
Emulate a call to getsockopt() on the socket associated
to bpf_socket, which must be a full socket. The level
at which the option resides and the name optname of the
option must be specified, see getsockopt(2) for more
information. The retrieved value is stored in the
structure pointed by opval and of length optlen.
This helper actually implements a subset of
getsockopt(). It supports the following levels:
· IPPROTO_TCP, which supports optnameTCP_CONGESTION.
· IPPROTO_IP, which supports optnameIP_TOS.
· IPPROTO_IPV6, which supports optnameIPV6_TCLASS.
Return 0 on success, or a negative error in case of failure.
int bpf_override_return(struct pt_reg *regs, u64 rc)Description
Used for error injection, this helper uses kprobes to
override the return value of the probed function, and
to set it to rc. The first argument is the context
regs on which the kprobe works.
This helper works by setting setting the PC (program
counter) to an override function which is run in place
of the original probed function. This means the probed
function is not run at all. The replacement function
just returns with the required value.
This helper has security implications, and thus is
subject to restrictions. It is only available if the
kernel was compiled with the CONFIG_BPF_KPROBE_OVERRIDE
configuration option, and in this case it only works on
functions tagged with ALLOW_ERROR_INJECTION in the
kernel code.
Also, the helper is only available for the
architectures having the
CONFIG_FUNCTION_ERROR_INJECTION option. As of this
writing, x86 architecture is the only one to support
this feature.
Returnint bpf_sock_ops_cb_flags_set(struct bpf_sock_ops *bpf_sock, intargval)Description
Attempt to set the value of the bpf_sock_ops_cb_flags
field for the full TCP socket associated to
bpf_sock_ops to argval.
The primary use of this field is to determine if there
should be calls to eBPF programs of type
BPF_PROG_TYPE_SOCK_OPS at various points in the TCP
code. A program of the same type can change its value,
per connection and as necessary, when the connection is
established. This field is directly accessible for
reading, but this helper must be used for updates in
order to return an error if an eBPF program tries to
set a callback that is not supported in the current
kernel.
The supported callback values that argval can combine
are:
· BPF_SOCK_OPS_RTO_CB_FLAG (retransmission time out)
· BPF_SOCK_OPS_RETRANS_CB_FLAG (retransmission)
· BPF_SOCK_OPS_STATE_CB_FLAG (TCP state change)
Here are some examples of where one could call such
eBPF program:
· When RTO fires.
· When a packet is retransmitted.
· When the connection terminates.
· When a packet is sent.
· When a packet is received.
Return Code -EINVAL if the socket is not a full TCP socket;
otherwise, a positive number containing the bits that
could not be set is returned (which comes down to 0 if
all bits were set as required).
int bpf_msg_redirect_map(struct sk_msg_buff *msg, struct bpf_map*map, u32 key, u64 flags)Description
This helper is used in programs implementing policies
at the socket level. If the message msg is allowed to
pass (i.e. if the verdict eBPF program returns
SK_PASS), redirect it to the socket referenced by map
(of type BPF_MAP_TYPE_SOCKMAP) at index key. Both
ingress and egress interfaces can be used for
redirection. The BPF_F_INGRESS value in flags is used
to make the distinction (ingress path is selected if
the flag is present, egress path otherwise). This is
the only flag supported for now.
Return SK_PASS on success, or SK_DROP on error.
int bpf_msg_apply_bytes(struct sk_msg_buff *msg, u32 bytes)Description
For socket policies, apply the verdict of the eBPF
program to the next bytes (number of bytes) of message
msg.
For example, this helper can be used in the following
cases:
· A single sendmsg() or sendfile() system call contains
multiple logical messages that the eBPF program is
supposed to read and for which it should apply a
verdict.
· An eBPF program only cares to read the first bytes of
a msg. If the message has a large payload, then
setting up and calling the eBPF program repeatedly
for all bytes, even though the verdict is already
known, would create unnecessary overhead.
When called from within an eBPF program, the helper
sets a counter internal to the BPF infrastructure, that
is used to apply the last verdict to the next bytes. If
bytes is smaller than the current data being processed
from a sendmsg() or sendfile() system call, the first
bytes will be sent and the eBPF program will be re-run
with the pointer for start of data pointing to byte
number bytes+ 1. If bytes is larger than the current
data being processed, then the eBPF verdict will be
applied to multiple sendmsg() or sendfile() calls until
bytes are consumed.
Note that if a socket closes with the internal counter
holding a non-zero value, this is not a problem because
data is not being buffered for bytes and is sent as it
is received.
Returnint bpf_msg_cork_bytes(struct sk_msg_buff *msg, u32 bytes)Description
For socket policies, prevent the execution of the
verdict eBPF program for message msg until bytes (byte
number) have been accumulated.
This can be used when one needs a specific number of
bytes before a verdict can be assigned, even if the
data spans multiple sendmsg() or sendfile() calls. The
extreme case would be a user calling sendmsg()
repeatedly with 1-byte long message segments.
Obviously, this is bad for performance, but it is still
valid. If the eBPF program needs bytes bytes to
validate a header, this helper can be used to prevent
the eBPF program to be called again until bytes have
been accumulated.
Returnint bpf_msg_pull_data(struct sk_msg_buff *msg, u32 start, u32 end,u64 flags)Description
For socket policies, pull in non-linear data from user
space for msg and set pointers msg->data and
msg->data_end to start and end bytes offsets into msg,
respectively.
If a program of type BPF_PROG_TYPE_SK_MSG is run on a
msg it can only parse data that the (data, data_end)
pointers have already consumed. For sendmsg() hooks
this is likely the first scatterlist element. But for
calls relying on the sendpage handler (e.g. sendfile())
this will be the range (0, 0) because the data is
shared with user space and by default the objective is
to avoid allowing user space to modify data while (or
after) eBPF verdict is being decided. This helper can
be used to pull in data and to set the start and end
pointer to given values. Data will be copied if
necessary (i.e. if data was not linear and if start and
end pointers do not point to the same chunk).
A call to this helper is susceptible to change the
underlaying packet buffer. Therefore, at load time, all
checks on pointers previously done by the verifier are
invalidated and must be performed again, if the helper
is used in combination with direct packet access.
All values for flags are reserved for future usage, and
must be left at zero.
Return 0 on success, or a negative error in case of failure.
int bpf_bind(struct bpf_sock_addr *ctx, struct sockaddr *addr, intaddr_len)Description
Bind the socket associated to ctx to the address
pointed by addr, of length addr_len. This allows for
making outgoing connection from the desired IP address,
which can be useful for example when all processes
inside a cgroup should use one single IP address on a
host that has multiple IP configured.
This helper works for IPv4 and IPv6, TCP and UDP
sockets. The domain (addr->sa_family) must be AF_INET
(or AF_INET6). Looking for a free port to bind to can
be expensive, therefore binding to port is not
permitted by the helper: addr->sin_port (or sin6_port,
respectively) must be set to zero.
Return 0 on success, or a negative error in case of failure.
int bpf_xdp_adjust_tail(struct xdp_buff *xdp_md, int delta)Description
Adjust (move) xdp_md->data_end by delta bytes. It is
only possible to shrink the packet as of this writing,
therefore delta must be a negative integer.
A call to this helper is susceptible to change the
underlaying packet buffer. Therefore, at load time, all
checks on pointers previously done by the verifier are
invalidated and must be performed again, if the helper
is used in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
int bpf_skb_get_xfrm_state(struct sk_buff *skb, u32 index, structbpf_xfrm_state *xfrm_state, u32 size, u64 flags)Description
Retrieve the XFRM state (IP transform framework, see
also ip-xfrm(8)) at index in XFRM "security path" for
skb.
The retrieved value is stored in the structbpf_xfrm_state pointed by xfrm_state and of length
size.
All values for flags are reserved for future usage, and
must be left at zero.
This helper is available only if the kernel was
compiled with CONFIG_XFRM configuration option.
Return 0 on success, or a negative error in case of failure.
int bpf_get_stack(struct pt_regs *regs, void *buf, u32 size, u64flags)Description
Return a user or a kernel stack in bpf program provided
buffer. To achieve this, the helper needs ctx, which
is a pointer to the context on which the tracing
program is executed. To store the stacktrace, the bpf
program provides buf with a nonnegative size.
The last argument, flags, holds the number of stack
frames to skip (from 0 to 255), masked with
BPF_F_SKIP_FIELD_MASK. The next bits can be used to set
the following flags:
BPF_F_USER_STACK
Collect a user space stack instead of a kernel
stack.
BPF_F_USER_BUILD_ID
Collect buildid+offset instead of ips for user
stack, only valid if BPF_F_USER_STACK is also
specified.
bpf_get_stack() can collect up to PERF_MAX_STACK_DEPTH
both kernel and user frames, subject to sufficient
large buffer size. Note that this limit can be
controlled with the sysctl program, and that it should
be manually increased in order to profile long user
stacks (such as stacks for Java programs). To do so,
use:
# sysctl kernel.perf_event_max_stack=<new value>
Return A non-negative value equal to or less than size on
success, or a negative error in case of failure.
int bpf_skb_load_bytes_relative(const struct sk_buff *skb, u32offset, void *to, u32 len, u32 start_header)Description
This helper is similar to bpf_skb_load_bytes() in that
it provides an easy way to load len bytes from offset
from the packet associated to skb, into the buffer
pointed by to. The difference to bpf_skb_load_bytes()
is that a fifth argument start_header exists in order
to select a base offset to start from. start_header can
be one of:
BPF_HDR_START_MAC
Base offset to load data from is skb's mac
header.
BPF_HDR_START_NET
Base offset to load data from is skb's network
header.
In general, "direct packet access" is the preferred
method to access packet data, however, this helper is
in particular useful in socket filters where skb->data
does not always point to the start of the mac header
and where "direct packet access" is not available.
Return 0 on success, or a negative error in case of failure.
int bpf_fib_lookup(void *ctx, struct bpf_fib_lookup *params, intplen, u32 flags)Description
Do FIB lookup in kernel tables using parameters in
params. If lookup is successful and result shows
packet is to be forwarded, the neighbor tables are
searched for the nexthop. If successful (ie., FIB
lookup shows forwarding and nexthop is resolved), the
nexthop address is returned in ipv4_dst or ipv6_dst
based on family, smac is set to mac address of egress
device, dmac is set to nexthop mac address, rt_metric
is set to metric from route (IPv4/IPv6 only), and
ifindex is set to the device index of the nexthop from
the FIB lookup.
plen argument is the size of the passed in struct.
flags argument can be a combination of one or more of
the following values:
BPF_FIB_LOOKUP_DIRECT
Do a direct table lookup vs full lookup using
FIB rules.
BPF_FIB_LOOKUP_OUTPUT
Perform lookup from an egress perspective
(default is ingress).
ctx is either struct xdp_md for XDP programs or structsk_buff tc cls_act programs.
Return
· < 0 if any input argument is invalid
· 0 on success (packet is forwarded, nexthop neighbor
exists)
· > 0 one of BPF_FIB_LKUP_RET_ codes explaining why the
packet is not forwarded or needs assist from full
stack
int bpf_sock_hash_update(struct bpf_sock_ops_kern *skops, structbpf_map *map, void *key, u64 flags)Description
Add an entry to, or update a sockhash map referencing
sockets. The skops is used as a new value for the
entry associated to key. flags is one of:
BPF_NOEXIST
The entry for key must not exist in the map.
BPF_EXIST
The entry for key must already exist in the map.
BPF_ANY
No condition on the existence of the entry for
key.
If the map has eBPF programs (parser and verdict),
those will be inherited by the socket being added. If
the socket is already attached to eBPF programs, this
results in an error.
Return 0 on success, or a negative error in case of failure.
int bpf_msg_redirect_hash(struct sk_msg_buff *msg, struct bpf_map*map, void *key, u64 flags)Description
This helper is used in programs implementing policies
at the socket level. If the message msg is allowed to
pass (i.e. if the verdict eBPF program returns
SK_PASS), redirect it to the socket referenced by map
(of type BPF_MAP_TYPE_SOCKHASH) using hash key. Both
ingress and egress interfaces can be used for
redirection. The BPF_F_INGRESS value in flags is used
to make the distinction (ingress path is selected if
the flag is present, egress path otherwise). This is
the only flag supported for now.
Return SK_PASS on success, or SK_DROP on error.
int bpf_sk_redirect_hash(struct sk_buff *skb, struct bpf_map *map,void *key, u64 flags)Description
This helper is used in programs implementing policies
at the skb socket level. If the sk_buff skb is allowed
to pass (i.e. if the verdeict eBPF program returns
SK_PASS), redirect it to the socket referenced by map
(of type BPF_MAP_TYPE_SOCKHASH) using hash key. Both
ingress and egress interfaces can be used for
redirection. The BPF_F_INGRESS value in flags is used
to make the distinction (ingress path is selected if
the flag is present, egress otherwise). This is the
only flag supported for now.
Return SK_PASS on success, or SK_DROP on error.
int bpf_lwt_push_encap(struct sk_buff *skb, u32 type, void *hdr, u32len)Description
Encapsulate the packet associated to skb within a Layer
3 protocol header. This header is provided in the
buffer at address hdr, with len its size in bytes. type
indicates the protocol of the header and can be one of:
BPF_LWT_ENCAP_SEG6
IPv6 encapsulation with Segment Routing Header
(struct ipv6_sr_hdr). hdr only contains the SRH,
the IPv6 header is computed by the kernel.
BPF_LWT_ENCAP_SEG6_INLINE
Only works if skb contains an IPv6 packet.
Insert a Segment Routing Header (structipv6_sr_hdr) inside the IPv6 header.
A call to this helper is susceptible to change the
underlaying packet buffer. Therefore, at load time, all
checks on pointers previously done by the verifier are
invalidated and must be performed again, if the helper
is used in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
int bpf_lwt_seg6_store_bytes(struct sk_buff *skb, u32 offset, constvoid *from, u32 len)Description
Store len bytes from address from into the packet
associated to skb, at offset. Only the flags, tag and
TLVs inside the outermost IPv6 Segment Routing Header
can be modified through this helper.
A call to this helper is susceptible to change the
underlaying packet buffer. Therefore, at load time, all
checks on pointers previously done by the verifier are
invalidated and must be performed again, if the helper
is used in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
int bpf_lwt_seg6_adjust_srh(struct sk_buff *skb, u32 offset, s32delta)Description
Adjust the size allocated to TLVs in the outermost IPv6
Segment Routing Header contained in the packet
associated to skb, at position offset by delta bytes.
Only offsets after the segments are accepted. delta can
be as well positive (growing) as negative (shrinking).
A call to this helper is susceptible to change the
underlaying packet buffer. Therefore, at load time, all
checks on pointers previously done by the verifier are
invalidated and must be performed again, if the helper
is used in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
int bpf_lwt_seg6_action(struct sk_buff *skb, u32 action, void *param,u32 param_len)Description
Apply an IPv6 Segment Routing action of type action to
the packet associated to skb. Each action takes a
parameter contained at address param, and of length
param_len bytes. action can be one of:
SEG6_LOCAL_ACTION_END_X
End.X action: Endpoint with Layer-3
cross-connect. Type of param: struct in6_addr.
SEG6_LOCAL_ACTION_END_T
End.T action: Endpoint with specific IPv6 table
lookup. Type of param: int.
SEG6_LOCAL_ACTION_END_B6
End.B6 action: Endpoint bound to an SRv6 policy.
Type of param: struct ipv6_sr_hdr.
SEG6_LOCAL_ACTION_END_B6_ENCAP
End.B6.Encap action: Endpoint bound to an SRv6
encapsulation policy. Type of param: structipv6_sr_hdr.
A call to this helper is susceptible to change the
underlaying packet buffer. Therefore, at load time, all
checks on pointers previously done by the verifier are
invalidated and must be performed again, if the helper
is used in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
int bpf_rc_keydown(void *ctx, u32 protocol, u64 scancode, u32 toggle)Description
This helper is used in programs implementing IR
decoding, to report a successfully decoded key press
with scancode, toggle value in the given protocol. The
scancode will be translated to a keycode using the rc
keymap, and reported as an input key down event. After
a period a key up event is generated. This period can
be extended by calling either bpf_rc_keydown() again
with the same values, or calling bpf_rc_repeat().
Some protocols include a toggle bit, in case the button
was released and pressed again between consecutive
scancodes.
The ctx should point to the lirc sample as passed into
the program.
The protocol is the decoded protocol number (see enumrc_proto for some predefined values).
This helper is only available is the kernel was
compiled with the CONFIG_BPF_LIRC_MODE2 configuration
option set to "y".
Returnint bpf_rc_repeat(void *ctx)Description
This helper is used in programs implementing IR
decoding, to report a successfully decoded repeat key
message. This delays the generation of a key up event
for previously generated key down event.
Some IR protocols like NEC have a special IR message
for repeating last button, for when a button is held
down.
The ctx should point to the lirc sample as passed into
the program.
This helper is only available is the kernel was
compiled with the CONFIG_BPF_LIRC_MODE2 configuration
option set to "y".
Returnuint64_t bpf_skb_cgroup_id(struct sk_buff *skb)Description
Return the cgroup v2 id of the socket associated with
the skb. This is roughly similar to the
bpf_get_cgroup_classid() helper for cgroup v1 by
providing a tag resp. identifier that can be matched on
or used for map lookups e.g. to implement policy. The
cgroup v2 id of a given path in the hierarchy is
exposed in user space through the f_handle API in order
to get to the same 64-bit id.
This helper can be used on TC egress path, but not on
ingress, and is available only if the kernel was
compiled with the CONFIG_SOCK_CGROUP_DATA configuration
option.
Return The id is returned or 0 in case the id could not be
retrieved.
u64 bpf_skb_ancestor_cgroup_id(struct sk_buff *skb, intancestor_level)Description
Return id of cgroup v2 that is ancestor of cgroup
associated with the skb at the ancestor_level. The
root cgroup is at ancestor_level zero and each step
down the hierarchy increments the level. If
ancestor_level == level of cgroup associated with skb,
then return value will be same as that of
bpf_skb_cgroup_id().
The helper is useful to implement policies based on
cgroups that are upper in hierarchy than immediate
cgroup associated with skb.
The format of returned id and helper limitations are
same as in bpf_skb_cgroup_id().
Return The id is returned or 0 in case the id could not be
retrieved.
u64 bpf_get_current_cgroup_id(void)Return A 64-bit integer containing the current cgroup id based
on the cgroup within which the current task is running.
void* get_local_storage(void *map, u64 flags)Description
Get the pointer to the local storage area. The type
and the size of the local storage is defined by the map
argument. The flags meaning is specific for each map
type, and has to be 0 for cgroup local storage.
Depending on the BPF program type, a local storage area
can be shared between multiple instances of the BPF
program, running simultaneously.
A user should care about the synchronization by
himself. For example, by using the BPF_STX_XADD
instruction to alter the shared data.
Return A pointer to the local storage area.
int bpf_sk_select_reuseport(struct sk_reuseport_md *reuse, structbpf_map *map, void *key, u64 flags)Description
Select a SO_REUSEPORT socket from a
BPF_MAP_TYPE_REUSEPORT_ARRAY map. It checks the
selected socket is matching the incoming request in the
socket buffer.
Return 0 on success, or a negative error in case of failure.
struct bpf_sock *bpf_sk_lookup_tcp(void *ctx, struct bpf_sock_tuple*tuple, u32 tuple_size, u64 netns, u64 flags)Description
Look for TCP socket matching tuple, optionally in a
child network namespace netns. The return value must be
checked, and if non-NULL, released via
bpf_sk_release().
The ctx should point to the context of the program,
such as the skb or socket (depending on the hook in
use). This is used to determine the base network
namespace for the lookup.
tuple_size must be one of:
sizeof(tuple->ipv4)
Look for an IPv4 socket.
sizeof(tuple->ipv6)
Look for an IPv6 socket.
If the netns is a negative signed 32-bit integer, then
the socket lookup table in the netns associated with
the ctx will will be used. For the TC hooks, this is
the netns of the device in the skb. For socket hooks,
this is the netns of the socket. If netns is any other
signed 32-bit value greater than or equal to zero then
it specifies the ID of the netns relative to the netns
associated with the ctx. netns values beyond the range
of 32-bit integers are reserved for future use.
All values for flags are reserved for future usage, and
must be left at zero.
This helper is available only if the kernel was
compiled with CONFIG_NET configuration option.
Return Pointer to struct bpf_sock, or NULL in case of failure.
For sockets with reuseport option, the struct bpf_sock
result is from reuse->socks[] using the hash of the
tuple.
struct bpf_sock *bpf_sk_lookup_udp(void *ctx, struct bpf_sock_tuple*tuple, u32 tuple_size, u64 netns, u64 flags)Description
Look for UDP socket matching tuple, optionally in a
child network namespace netns. The return value must be
checked, and if non-NULL, released via
bpf_sk_release().
The ctx should point to the context of the program,
such as the skb or socket (depending on the hook in
use). This is used to determine the base network
namespace for the lookup.
tuple_size must be one of:
sizeof(tuple->ipv4)
Look for an IPv4 socket.
sizeof(tuple->ipv6)
Look for an IPv6 socket.
If the netns is a negative signed 32-bit integer, then
the socket lookup table in the netns associated with
the ctx will will be used. For the TC hooks, this is
the netns of the device in the skb. For socket hooks,
this is the netns of the socket. If netns is any other
signed 32-bit value greater than or equal to zero then
it specifies the ID of the netns relative to the netns
associated with the ctx. netns values beyond the range
of 32-bit integers are reserved for future use.
All values for flags are reserved for future usage, and
must be left at zero.
This helper is available only if the kernel was
compiled with CONFIG_NET configuration option.
Return Pointer to struct bpf_sock, or NULL in case of failure.
For sockets with reuseport option, the struct bpf_sock
result is from reuse->socks[] using the hash of the
tuple.
int bpf_sk_release(struct bpf_sock *sock)Description
Release the reference held by sock. sock must be a
non-NULL pointer that was returned from
bpf_sk_lookup_xxx().
Return 0 on success, or a negative error in case of failure.
int bpf_map_pop_elem(struct bpf_map *map, void *value)Description
Pop an element from map.
Return 0 on success, or a negative error in case of failure.
int bpf_map_peek_elem(struct bpf_map *map, void *value)Description
Get an element from map without removing it.
Return 0 on success, or a negative error in case of failure.
int bpf_msg_push_data(struct sk_buff *skb, u32 start, u32 len, u64flags)Description
For socket policies, insert len bytes into msg at
offset start.
If a program of type BPF_PROG_TYPE_SK_MSG is run on a
msg it may want to insert metadata or options into the
msg. This can later be read and used by any of the
lower layer BPF hooks.
This helper may fail if under memory pressure (a malloc
fails) in these cases BPF programs will get an
appropriate error and BPF programs will need to handle
them.
Return 0 on success, or a negative error in case of failure.
int bpf_msg_pop_data(struct sk_msg_buff *msg, u32 start, u32 pop, u64flags)Description
Will remove pop bytes from a msg starting at byte
start. This may result in ENOMEM errors under certain
situations if an allocation and copy are required due
to a full ring buffer. However, the helper will try to
avoid doing the allocation if possible. Other errors
can occur if input parameters are invalid either due to
start byte not being valid part of msg payload and/or
pop value being to large.
Return 0 on success, or a negative error in case of failure.
int bpf_rc_pointer_rel(void *ctx, s32 rel_x, s32 rel_y)Description
This helper is used in programs implementing IR
decoding, to report a successfully decoded pointer
movement.
The ctx should point to the lirc sample as passed into
the program.
This helper is only available is the kernel was
compiled with the CONFIG_BPF_LIRC_MODE2 configuration
option set to "y".
Return

eBPF programs can have an associated license, passed along with the
bytecode instructions to the kernel when the programs are loaded. The
format for that string is identical to the one in use for kernel
modules (Dual licenses, such as "Dual BSD/GPL", may be used). Some
helper functions are only accessible to programs that are compatible
with the GNU Privacy License (GPL).
In order to use such helpers, the eBPF program must be loaded with
the correct license string passed (via attr) to the bpf() system
call, and this generally translates into the C source code of the
program containing a line similar to the following:
char ____license[] __attribute__((section("license"), used)) = "GPL";

This manual page is an effort to document the existing eBPF helper
functions. But as of this writing, the BPF sub-system is under heavy
development. New eBPF program or map types are added, along with new
helper functions. Some helpers are occasionally made available for
additional program types. So in spite of the efforts of the
community, this page might not be up-to-date. If you want to check by
yourself what helper functions exist in your kernel, or what types of
programs they can support, here are some files among the kernel tree
that you may be interested in:
· include/uapi/linux/bpf.h is the main BPF header. It contains the
full list of all helper functions, as well as many other BPF
definitions including most of the flags, structs or constants used
by the helpers.
· net/core/filter.c contains the definition of most network-related
helper functions, and the list of program types from which they can
be used.
· kernel/trace/bpf_trace.c is the equivalent for most tracing
program-related helpers.
· kernel/bpf/verifier.c contains the functions used to check that
valid types of eBPF maps are used with a given helper function.
· kernel/bpf/ directory contains other files in which additional
helpers are defined (for cgroups, sockmaps, etc.).
Compatibility between helper functions and program types can
generally be found in the files where helper functions are defined.
Look for the struct bpf_func_proto objects and for functions
returning them: these functions contain a list of helpers that a
given program type can call. Note that the default: label of the
switch ... case used to filter helpers can call other functions,
themselves allowing access to additional helpers. The requirement for
GPL license is also in those struct bpf_func_proto.
Compatibility between helper functions and map types can be found in
the check_map_func_compatibility() function in file
kernel/bpf/verifier.c.
Helper functions that invalidate the checks on data and data_end
pointers for network processing are listed in function
bpf_helper_changes_pkt_data() in file net/core/filter.c.

This page is part of release 5.00 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
Linux 2019-03-06 BPF-HELPERS(7)